ABSTRACT: The normal balance between coagulation and fibrinolysis, both intravascularly and extravascularly, is significantly altered during pulmonary injuries. The coagulation pathway is activated that is accompanied by an inhibition of fibrinolytic activity. This imbalance leads to fibrin deposition in the alveolar, interstitial and vascular spaces of the lung, thereby adversely affecting cardiovascular and respiratory functions. In addition to impaired blood perfusion and gas exchange due to clot formation, fibrin also promotes an acute cellular inflammatory response, contributes to surfactant dysfunction and provides a provisional matrix for collagen deposition in the lung. Thus, decreasing fibrin deposition within the lung is not only important for the improvement of hemodynamics and prevention of pulmonary damage at the early stages of pulmonary injury but also beneficial for the prevention of late-stage fibrosis. We propose in this application to develop a novel and safe nonviral vector for pulmonary uPA gene transfer for the treatment of pulmonary injury. Our basic hypothesis is that systemic delivery of uPA gene to the lung would upregulate the fibrinolytic activity within the lung and reduce collagen accumulation that follows pulmonary inflammation. Accordingly, specific aims of this comprehensive proposal are: Aim 1: To develop a novel polymer-based delivery system that is highly efficient in selective gene delivery to pulmonary circulation with minimal toxicity. Aim 2: To develop a mini/mutated uPA that fully retains its proteolytic activity but lacks pro-inflammatory activity. Aim 3: To study the biological consequences of expressed uPA following pulmonary uPA gene transfer. Aim 4: To examine the therapeutic efficacy of uPA gene transfer in a mouse model of bleomycin-induced pulmonary injury. Completion of the above studies will lead to development of a novel therapy that will be beneficial not only for the treatment of acute lung injury but also for the prevention and treatment of late-stage complications such as pulmonary fibrosis. The novel nonviral vectors developed in this application can also be readily employed for targeted delivery of different therapeutic genes for the treatment of other pulmonary diseases such as pulmonary hypertension.